The present invention broadly relates to a method and apparatus for fabricating involute gear tooth flanks.
Generally speaking, the invention relates to a method for fabricating involute gear tooth flanks without or with geometric corrections by means of at least one machining tool and in which method machining, feed and traversing motions between the machining tool and a workpiece or gear blank are performed.
The invention is also concerned with a machine tool or machining apparatus for performing the method and comprising a machine frame with a generating carriage translatably seated on this machine frame. The machine tool or machining apparatus further comprises a workpiece or gear blank carrier or support and clamping means for holding a workpiece or gear blank and a multiple-carriage or carriage-and-slide arrangement for performing the machining, traversing and feed motions. Drive means as well as control means for carrying out, i.e. controlling and powering, these movements are also provided.
In a known method of fabricating involute gear tooth flanks, conical or dished grinding wheels are used which each respectively process a right and a left gear tooth flank. For this purpose, the two grinding wheels are fixed at an angle in relation to each other such that working or machining planes of the grinding wheels define the surfaces of a hypothetical generating rack on which the gear to be ground is generated or rolled. The inclination of the grinding wheels to a normal to the generating roll plane or pitch plane is generally the same as the pressure angle of the gear teeth. The relative motion between the machining tool or grinding wheel and the workpiece or gear blank for generating the involute form, the so-called generating roll motion, is derived from the pitch circle. FIG. 6 hereof shows the generating process of a gear wheel on a hypothetical rack in transverse section and in a number of phases. The points A, P, C, T and E' delimit segments of the line of action which correspond to regions of the tooth flank. The addendum flank or flank region is formed on the tooth flank during the grinding process when the section AC of the line of action is traversed. When the section CT of the line of action is traversed, then an initial or outer dedendum flank or flank region of the tooth flank involute is correspondingly formed.
The point T on the line of action is reached when the corner point K of the basic tooth rack profile lies on the line of centers OC connecting the workpiece or gear blank center 0 with the pitch point C on the line of action. The section TE of the line of action corresponds to two segments on the tooth flank which are formed simultaneously (cf. FIG. 11): a further or inner dedendum flank portion of the tooth flank involute and a trochoidal or undercut dedendum or root fillet radius. The point E is the lowest or innermost point of the involute and at the same time the initial point of the dedendum or root fillet trochoid or undercut. The curves or semicircles shown in dotted lines in FIG. 11 indicate which points of the inner dedendum flank portion of the tooth involute and of the dedendum fillet or undercut are simultaneously generated.
FIG. 16 shows the working or machining points Pi', Pi" on a dished or flat grinding wheel or disk which is in contact with the tooth flank of the workpiece or gear blank. During the grinding process, these working or machining points wander, depending upon the generating roll position i, along the machining or grinding surface of the disk and the edges of the grinding wheel and each such working or machining point lies on a generatrix of the tooth flank surface.
During the generating process, a working or machining point of a conical or beveled grinding wheel will wander along a meridian over a working or machining width of the grinding disk corresponding to the entire tooth flank. Machines or apparatus for such a process are, for example, described in the Swiss Pat. No. 592,604 granted Oct. 31, 1972, and the German Pat. No. 2,050,946, granted May 13, 1976. It is a disadvantage of this process that topological or geometric flank corrections can only be carried out to a relatively limited extent since due to the forces which arise between the workpiece or gear blank and the machining tool and other system conditions relative to the size of the gear tooth in general, a larger area of the grinding wheel or disk is involved in the machining process producing the involute form. The working or machining regions especially can only be very coarsely localized and can be influenced only by altering system features which are very difficult or impossible to carry out, such as grinding wheel size or shape.